The interaction of HDL apolipoproteins, particularly apoA-I, with the cell membrane transporter ABCA1[unreadable] removes excess cellular cholesterol and protects against atherogenesis. This process is mediated by lipidpoor[unreadable] apolipoproteins generated by either de novo synthesis or dissociation from HDL particles. Thus, factors[unreadable] that impair the generation or lipid efflux activity of apoA-I could have profound atherogenic effects. Oxidative[unreadable] damage is implicated in the pathogenesis of atherosclerosis, a chronic inflammatory disease. 3-[unreadable] Chlorotyrosine and 3-nitrotyrosine, stable products of protein oxidation generated by phagocyte-derived[unreadable] hypochlorous acid (HOCI) and reactive nitrogen species (RNS), have been detected in human[unreadable] atherosclerotic lesions. However, the underlying factors that control tyrosine oxidation in proteins remain[unreadable] poorly understood. We found that oxidation of apoA-I by HOCI severely impairs its ability to remove cellular[unreadable] cholesterol by the ABCA1 pathway, consistent with the possibility that oxidation of HDL apolipoproteins in[unreadable] vivo would be atherogenic. We propose to test the hypothesis that site-specific oxidation of tyrosine[unreadable] residues by phagocyte-derived HOCI and RNS alters the biological and atheroprotective function of HDL.[unreadable] We will characterize the effects of site-specific oxidation of tyrosines in apoA-I on its ability to remove cellular[unreadable] cholesterol, identify protein motifs that direct site-specific tyrosine oxidation by HOCI and RNS, and[unreadable] determine if HDL is a physiological target for oxidative modification in the artery wall. This project will use[unreadable] HPLC and tandem mass spectrometry to locate and quantify the sites of tyrosine oxidation in apoA-I and[unreadable] model peptides, cell biology procedures to characterize the effects of apoA-I oxidation on lipid transport[unreadable] activity and interactions with ABCA1, tissue analysis to identify and characterize oxidized apoA-I in human[unreadable] atherosclerotic lesions, and mouse model approaches to test for the effects of macrophage-generated HOCI[unreadable] on apoA-I oxidation and atherogenesis in vivo. The proposed studies will provide insights into the structural[unreadable] features that direct oxidative modification of proteins, with important implications for the physiological[unreadable] significance of oxidative reactions in atherosclerosis and other inflammatory diseases.